This invention generally relates to a compressor for a vapor compression system, and specifically to a compressor for a vapor compressor system including an oil separator.
Compressors employ a motor for driving a pump mechanism to compress fluid and, therefore, typically contain lubricant for reducing friction between sliding surfaces. In hermetic or semi-hermetic compressors, an electric motor drives the pump mechanism through a driveline assembly. Refrigerant from the vapor compression system may flow over and around the motor and portions of the driveline. Lubricant typically flows through and around portions of the driveline to lubricate the sliding surfaces.
Although the primary lubricant flow path is mostly separate from the refrigerant flow path, some lubricant still can become mixed with the refrigerant. Lubricant mixed in with the refrigerant can reduce efficiency and reliability of the vapor compression system. Lubricant carried along with the refrigerant flow can inhibit heat transfer and reduce the effectiveness of heat exchangers. Further, lubricant carried with the refrigerant can plug small holes and inhibit performance of system components such as expanders. In addition, lubricant carried with the refrigerant can accumulate in unwanted or unexpected places within the compression system and may result in a loss of lubricant available for reducing friction and wear inside the compressor, thus reducing reliability.
A transcritical vapor compression system includes a refrigerant exiting the compressor in a supercritical state. Refrigerant enters the compressor in a low-pressure state and commonly flows over the electric motor to aid in cooling the motor and reducing its operating temperature. Oil from the driveline can mix with the refrigerant and enter a compression chamber with the refrigerant. It is common to employ an oil-separating device to separate the oil from the refrigerant. Typically, an oil-separating device is employed after the compression chamber in the high-pressure portion of the system. In a transcritical system, this in the supercritical state. Oil separators typically include a passage for draining oil back to an oil sump on the low-pressure, sub-critical portion of the vapor compression system. This passage creates a constant leak within the vapor compression system that can reduce system efficiency.
Oil separators disposed after the compression chamber must include relatively thicker walls, and high-pressure seals to accommodated the greater pressures. Further, refrigerants in a super-critical state, particularly carbon dioxide, tend to be extremely soluble. This causes oil to be saturated within the supercritical refrigerant. Oil saturated within the super critical refrigerant is very difficult to remove efficiently. The difficulties caused by the use of an oil separator on the supercritical side of a vapor compression system limit some systems to run entirely below a critical point. This can limit the type of refrigerant utilized in the system.
Accordingly, it is desirable to develop a low-pressure side oil separator for separating oil from refrigerant.